The detection of the disease tuberculosis is usually performed by culturing a specimen from a suspected host in a medium referred to in the art as the Lowenstein-Jensen medium, or modifications thereof. The culture is incubated and the M. tuberculosis organisms develop to the substantial exclusion of other organisms. Thus, a positive test for tuberculosis is provided.
While this test is quite accurate and is widely practiced, the test has a decided disadvantage in that the Lowenstein-Jensen medium is not storage stable at ambient temperatures and even when refrigerated must be used within 30 days of preparation. In view thereof, it has been the practice in the art to use the Lowenstein-Jensen medium within a relatively short period after preparation. The preparation of the Lowenstein-Jensen medium is quite time consuming and, therefore, the use of the Lowenstein-Jensen medium has mainly been restricted to organizations which conduct sufficient tuberculosis test as to justify the repeated time-consuming preparations of the Lowenstein-Jensen medium. The occasional tester or the smaller institution cannot economically test for tuberculosis, due to the difficulty and expense of frequently preparing fresh medium.
A basic ingredient in the Lowenstein-Jensen medium is fresh whole eggs, e.g., eggs no older than three days. The medium must be prepared in a specific manner with specific nutrients/salts/inhibitors and fresh whole eggs, as is well known in the art. If the medium is not used within a relatively short time after preparation (even if refrigerated), the results obtained therewith are questionable. Attempts in the art at extending the useful life of a prepared Lowenstein-Jensen medium have not met with success and the most common expedient is to premix the dry ingredients in a sterile manner and to place the fresh eggs in the dry mixture when the medium is to be prepared.
In the parent application, identified above, it is disclosed that freshly prepared Lowenstein-Jensen medium can be stabilized for extended ambient storage by spray-drying that freshly prepared medium under such specific and critical conditions as to avoid deterioration of the dried product. The spray-drying technique is taught to be unique in drying procedures, in this regard, i.e. as opposed to tray drying, roller drying, etc.. It is also taught that the Lowenstein-Jensen medium, spray-dried in that specific manner, will remain storage stable for extended periods of time and may be conveniently reconstituted with water for testing for tuberculosis organisms. That parent application also teaches that even after prolonged periods of storage, the spray-dried medium can be reconstituted and used for testing for tuberculosis organisms. The primary basis of that conclusion was in vitro testing where the dried medium, after prolonged storage periods, was reconstituted and was shown to be capable of growing M. tuberculosis organisms.
However, clinical trials of the spray-dried Lowenstein-Jensen medium have discovered that the reconstituted spray-dried material is not as accurate as the freshly prepared medium. Indeed, the accuracy occasioned by the reconstituted spray-dried medium is decreased to approximately 75% as accurate as the fresh medium.
It has now been determined that the population of tuberculosis organisms in a clinical specimen may be considerably lower than the normal populations encountered in stock cultures used in in vitro testing. Thus, while the spray-dried material is quite accurate in testing specimens with relatively large numbers of tuberculosis organisms therein, its accuracy substantially decreases when the population of the organisms decreases. This is often the case encountered in clinical specimens and, hence, decreased accuracy in the clinical situation is experienced.
It has also been discovered that in order to simulate the problem encountered in clinical situations by in vitro testing, the normal stock solutions of tuberculosis organisms must be diluted in the order of at least 10.sup.3. If adequate growth takes place at these low dilutions, then the medium is satisfactory for clinical use.